1. Field of Invention
The present invention relates to a method for manufacturing a bone screw, and a tool for mounting and removing the bone screw, and more particularly to a bone screw where the Young's modulus of a shaft portion is smaller than that of a front portion and that of a rear portion.
2. Related Art
The work and life style in most areas of Asia is characterized in high population density, a great many motor vehicles, intensive labor forces, and gradually aging population. In recent years, the Asian economic environment and conditions are improved. In addition, the Asian body type is different from that of the westerners, and the causes of bone trauma in Asia are different from those in Europe and America which are mainly sports injuries. Therefore, the innovation and researches for bone trauma treatment products and equipment related to bone surgeries become more and more important in Asia.
Referring to FIG. 1, U.S. Pat. No. 4,175,555 discloses a bone screw 10. The bone screw 10 includes a front portion 20, a rear portion 30, and a shaft portion 40. The shaft portion 40 is located between the front portion 20 and the rear portion 30. The front portion 20 and the rear portion 30 of the bone screw 10 each have a thread with a different pitch and diameter, and are capable of compressing and drawing together two screwed bones. However, the shaft portion, the front portion, and the rear portion of the bone screw are integrally formed and manufactured with the same metal material, which fails to provide a relative micro-motion and an external buffer force between the two bones, and may further result in joint dislocation for a second time or uncompleted bone reposition when patients do exercise after the surgeries.
Referring to FIG. 2, U.S. Pat. No. 7,625,395 discloses an implantable screw 60 for stabilization of a joint or a bone fracture. The implantable screw 60 includes a front portion 70, a rear portion 80, and a flexible shaft portion 90. The flexible shaft portion 90, located between the front portion 70 and the rear portion 80, is capable of preventing axial tension between the front portion 70 and the rear portion 80, but allows small displacement in other directions. The flexible shaft portion 90 is formed by multiple sutures, instead of a hollow cylinder structure, and is not fixedly connected to the front portion 70 and the rear portion 80. However, in the foregoing patent, as the front portion and the rear portion are merely connected by using surgical sutures, the surgery process is complicated, a large wound needs to be opened to perform an operation, and the fixation strength is undesirable.
Therefore, it is required to provide a bone screw capable of solving the foregoing problems.